diff --git a/client/src/i18n/translations/ar.ts b/client/src/i18n/translations/ar.ts
index 390b05c0..99295939 100644
--- a/client/src/i18n/translations/ar.ts
+++ b/client/src/i18n/translations/ar.ts
@@ -464,6 +464,8 @@ const ar: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'تحقق',
   'login.invalidInviteLink': 'رابط الدعوة غير صالح أو منتهي الصلاحية',
   'login.oidcFailed': 'فشل تسجيل الدخول عبر OIDC',
+  'login.configLoadError': 'تعذّر تحميل خيارات تسجيل الدخول.',
+  'login.configLoadRetry': 'تحديث',
   'login.usernameRequired': 'اسم المستخدم مطلوب',
   'login.passwordMinLength': 'يجب أن تكون كلمة المرور 8 أحرف على الأقل',
   'login.forgotPassword': 'نسيت كلمة المرور؟',
diff --git a/client/src/i18n/translations/br.ts b/client/src/i18n/translations/br.ts
index 0757c3d2..e23ca5a1 100644
--- a/client/src/i18n/translations/br.ts
+++ b/client/src/i18n/translations/br.ts
@@ -459,6 +459,8 @@ const br: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Verificar',
   'login.invalidInviteLink': 'Link de convite inválido ou expirado',
   'login.oidcFailed': 'Falha no login OIDC',
+  'login.configLoadError': 'Não foi possível carregar as opções de login.',
+  'login.configLoadRetry': 'Atualizar',
   'login.usernameRequired': 'Nome de usuário é obrigatório',
   'login.passwordMinLength': 'A senha deve ter pelo menos 8 caracteres',
   'login.forgotPassword': 'Esqueceu a senha?',
diff --git a/client/src/i18n/translations/cs.ts b/client/src/i18n/translations/cs.ts
index a14b633d..cc951bce 100644
--- a/client/src/i18n/translations/cs.ts
+++ b/client/src/i18n/translations/cs.ts
@@ -459,6 +459,8 @@ const cs: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Ověřit',
   'login.invalidInviteLink': 'Neplatný nebo vypršelý odkaz s pozvánkou',
   'login.oidcFailed': 'Přihlášení přes OIDC se nezdařilo',
+  'login.configLoadError': 'Nepodařilo se načíst možnosti přihlášení.',
+  'login.configLoadRetry': 'Obnovit',
   'login.usernameRequired': 'Uživatelské jméno je povinné',
   'login.passwordMinLength': 'Heslo musí mít alespoň 8 znaků',
   'login.forgotPassword': 'Zapomenuté heslo?',
diff --git a/client/src/i18n/translations/de.ts b/client/src/i18n/translations/de.ts
index cbb6d153..1aab8743 100644
--- a/client/src/i18n/translations/de.ts
+++ b/client/src/i18n/translations/de.ts
@@ -464,6 +464,8 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Bestätigen',
   'login.invalidInviteLink': 'Ungültiger oder abgelaufener Einladungslink',
   'login.oidcFailed': 'OIDC-Anmeldung fehlgeschlagen',
+  'login.configLoadError': 'Anmeldeoptionen konnten nicht geladen werden.',
+  'login.configLoadRetry': 'Aktualisieren',
   'login.usernameRequired': 'Benutzername ist erforderlich',
   'login.passwordMinLength': 'Das Passwort muss mindestens 8 Zeichen lang sein',
   'login.forgotPassword': 'Passwort vergessen?',
diff --git a/client/src/i18n/translations/en.ts b/client/src/i18n/translations/en.ts
index ce8321a6..145c6c5b 100644
--- a/client/src/i18n/translations/en.ts
+++ b/client/src/i18n/translations/en.ts
@@ -537,6 +537,8 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Verify',
   'login.invalidInviteLink': 'Invalid or expired invite link',
   'login.oidcFailed': 'OIDC login failed',
+  'login.configLoadError': 'Could not load login options.',
+  'login.configLoadRetry': 'Refresh',
   'login.usernameRequired': 'Username is required',
   'login.passwordMinLength': 'Password must be at least 8 characters',
   'login.forgotPassword': 'Forgot password?',
diff --git a/client/src/i18n/translations/es.ts b/client/src/i18n/translations/es.ts
index a66bdfb6..a4562409 100644
--- a/client/src/i18n/translations/es.ts
+++ b/client/src/i18n/translations/es.ts
@@ -451,6 +451,8 @@ const es: Record<string, string> = {
   'login.mfaVerify': 'Verificar',
   'login.invalidInviteLink': 'Enlace de invitación inválido o expirado',
   'login.oidcFailed': 'Error de inicio de sesión OIDC',
+  'login.configLoadError': 'No se pudieron cargar las opciones de inicio de sesión.',
+  'login.configLoadRetry': 'Actualizar',
   'login.usernameRequired': 'El nombre de usuario es obligatorio',
   'login.passwordMinLength': 'La contraseña debe tener al menos 8 caracteres',
   'login.forgotPassword': '¿Olvidaste tu contraseña?',
diff --git a/client/src/i18n/translations/fr.ts b/client/src/i18n/translations/fr.ts
index c7cd1605..ef26c1df 100644
--- a/client/src/i18n/translations/fr.ts
+++ b/client/src/i18n/translations/fr.ts
@@ -452,6 +452,8 @@ const fr: Record<string, string> = {
   'login.mfaVerify': 'Vérifier',
   'login.invalidInviteLink': 'Lien d\'invitation invalide ou expiré',
   'login.oidcFailed': 'Échec de connexion OIDC',
+  'login.configLoadError': 'Impossible de charger les options de connexion.',
+  'login.configLoadRetry': 'Actualiser',
   'login.usernameRequired': 'Le nom d\'utilisateur est obligatoire',
   'login.passwordMinLength': 'Le mot de passe doit comporter au moins 8 caractères',
   'login.forgotPassword': 'Mot de passe oublié ?',
diff --git a/client/src/i18n/translations/hu.ts b/client/src/i18n/translations/hu.ts
index f8046fab..a07397d5 100644
--- a/client/src/i18n/translations/hu.ts
+++ b/client/src/i18n/translations/hu.ts
@@ -459,6 +459,8 @@ const hu: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Ellenőrzés',
   'login.invalidInviteLink': 'Érvénytelen vagy lejárt meghívólink',
   'login.oidcFailed': 'OIDC bejelentkezés sikertelen',
+  'login.configLoadError': 'A bejelentkezési lehetőségek betöltése nem sikerült.',
+  'login.configLoadRetry': 'Frissítés',
   'login.usernameRequired': 'A felhasználónév kötelező',
   'login.passwordMinLength': 'A jelszónak legalább 8 karakter hosszúnak kell lennie',
   'login.forgotPassword': 'Elfelejtetted a jelszavad?',
diff --git a/client/src/i18n/translations/id.ts b/client/src/i18n/translations/id.ts
index 112d17fc..f9e51bb3 100644
--- a/client/src/i18n/translations/id.ts
+++ b/client/src/i18n/translations/id.ts
@@ -521,6 +521,8 @@ const id: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Verifikasi',
   'login.invalidInviteLink': 'Tautan undangan tidak valid atau sudah kedaluwarsa',
   'login.oidcFailed': 'Login OIDC gagal',
+  'login.configLoadError': 'Gagal memuat opsi login.',
+  'login.configLoadRetry': 'Segarkan',
   'login.usernameRequired': 'Nama pengguna wajib diisi',
   'login.passwordMinLength': 'Kata sandi minimal 8 karakter',
   'login.forgotPassword': 'Lupa kata sandi?',
diff --git a/client/src/i18n/translations/it.ts b/client/src/i18n/translations/it.ts
index 2ac5424f..44bdcfe8 100644
--- a/client/src/i18n/translations/it.ts
+++ b/client/src/i18n/translations/it.ts
@@ -459,6 +459,8 @@ const it: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Verifica',
   'login.invalidInviteLink': 'Link di invito non valido o scaduto',
   'login.oidcFailed': 'Accesso OIDC non riuscito',
+  'login.configLoadError': 'Impossibile caricare le opzioni di accesso.',
+  'login.configLoadRetry': 'Aggiorna',
   'login.usernameRequired': 'Il nome utente è obbligatorio',
   'login.passwordMinLength': 'La password deve contenere almeno 8 caratteri',
   'login.forgotPassword': 'Password dimenticata?',
diff --git a/client/src/i18n/translations/nl.ts b/client/src/i18n/translations/nl.ts
index 0cb55bc1..c16c68cb 100644
--- a/client/src/i18n/translations/nl.ts
+++ b/client/src/i18n/translations/nl.ts
@@ -452,6 +452,8 @@ const nl: Record<string, string> = {
   'login.mfaVerify': 'Verifiëren',
   'login.invalidInviteLink': 'Ongeldige of verlopen uitnodigingslink',
   'login.oidcFailed': 'OIDC-aanmelding mislukt',
+  'login.configLoadError': 'Kan aanmeldingsopties niet laden.',
+  'login.configLoadRetry': 'Vernieuwen',
   'login.usernameRequired': 'Gebruikersnaam is vereist',
   'login.passwordMinLength': 'Wachtwoord moet minimaal 8 tekens bevatten',
   'login.forgotPassword': 'Wachtwoord vergeten?',
diff --git a/client/src/i18n/translations/pl.ts b/client/src/i18n/translations/pl.ts
index 87f768a9..005541ae 100644
--- a/client/src/i18n/translations/pl.ts
+++ b/client/src/i18n/translations/pl.ts
@@ -426,6 +426,8 @@ const pl: Record<string, string | { name: string; category: string }[]> = {
   'login.mfaVerify': 'Weryfikuj',
   'login.invalidInviteLink': 'Nieprawidłowy lub wygasły link zaproszenia',
   'login.oidcFailed': 'Logowanie OIDC nie powiodło się',
+  'login.configLoadError': 'Nie można załadować opcji logowania.',
+  'login.configLoadRetry': 'Odśwież',
   'login.usernameRequired': 'Nazwa użytkownika jest wymagana',
   'login.passwordMinLength': 'Hasło musi mieć co najmniej 8 znaków',
   'login.forgotPassword': 'Nie pamiętasz hasła?',
diff --git a/client/src/i18n/translations/ru.ts b/client/src/i18n/translations/ru.ts
index f4f23fb8..0f82d22a 100644
--- a/client/src/i18n/translations/ru.ts
+++ b/client/src/i18n/translations/ru.ts
@@ -452,6 +452,8 @@ const ru: Record<string, string> = {
   'login.mfaVerify': 'Подтвердить',
   'login.invalidInviteLink': 'Недействительная или истёкшая ссылка-приглашение',
   'login.oidcFailed': 'Ошибка входа через OIDC',
+  'login.configLoadError': 'Не удалось загрузить параметры входа.',
+  'login.configLoadRetry': 'Обновить',
   'login.usernameRequired': 'Имя пользователя обязательно',
   'login.passwordMinLength': 'Пароль должен содержать не менее 8 символов',
   'login.forgotPassword': 'Забыли пароль?',
diff --git a/client/src/i18n/translations/zh.ts b/client/src/i18n/translations/zh.ts
index ffa564b6..72e9e9d2 100644
--- a/client/src/i18n/translations/zh.ts
+++ b/client/src/i18n/translations/zh.ts
@@ -452,6 +452,8 @@ const zh: Record<string, string> = {
   'login.mfaVerify': '验证',
   'login.invalidInviteLink': '邀请链接无效或已过期',
   'login.oidcFailed': 'OIDC 登录失败',
+  'login.configLoadError': '无法加载登录选项。',
+  'login.configLoadRetry': '刷新',
   'login.usernameRequired': '用户名为必填项',
   'login.passwordMinLength': '密码至少需要8个字符',
   'login.forgotPassword': '忘记密码？',
diff --git a/client/src/i18n/translations/zhTw.ts b/client/src/i18n/translations/zhTw.ts
index 331596c5..276a76f6 100644
--- a/client/src/i18n/translations/zhTw.ts
+++ b/client/src/i18n/translations/zhTw.ts
@@ -511,6 +511,8 @@ const zhTw: Record<string, string> = {
   'login.mfaVerify': '驗證',
   'login.invalidInviteLink': '邀請連結無效或已過期',
   'login.oidcFailed': 'OIDC 登入失敗',
+  'login.configLoadError': '無法載入登入選項。',
+  'login.configLoadRetry': '重新整理',
   'login.usernameRequired': '使用者名稱為必填',
   'login.passwordMinLength': '密碼至少需要8個字元',
   'login.forgotPassword': '忘記密碼？',
diff --git a/client/src/pages/LoginPage.tsx b/client/src/pages/LoginPage.tsx
index 6fa2c192..0104f97e 100644
--- a/client/src/pages/LoginPage.tsx
+++ b/client/src/pages/LoginPage.tsx
@@ -33,6 +33,7 @@ export default function LoginPage(): React.ReactElement {
   const [isLoading, setIsLoading] = useState<boolean>(false)
   const [error, setError] = useState<string>('')
   const [appConfig, setAppConfig] = useState<AppConfig | null>(null)
+  const [configError, setConfigError] = useState<boolean>(false)
   const [inviteToken, setInviteToken] = useState<string>('')
   const [inviteValid, setInviteValid] = useState<boolean>(false)
   const exchangeInitiated = useRef(false)
@@ -117,15 +118,15 @@ export default function LoginPage(): React.ReactElement {
       return
     }
 
-    authApi.getAppConfig?.().catch(() => null).then((config: AppConfig | null) => {
-      if (config) {
+    authApi.getAppConfig?.()
+      .then((config: AppConfig) => {
         setAppConfig(config)
         if (!config.has_users) setMode('register')
         if (!config.password_login && config.oidc_login && config.oidc_configured && config.has_users && !invite && !noRedirect) {
           window.location.href = '/api/auth/oidc/login'
         }
-      }
-    })
+      })
+      .catch(() => setConfigError(true))
   }, [navigate, t, noRedirect])
 
   // Language detection chain (runs once on mount, only if user has no saved preference):
@@ -860,6 +861,20 @@ export default function LoginPage(): React.ReactElement {
             </>
           )}
 
+          {/* Config load error — shown when /api/auth/app-config fails (e.g. ZT redirect,
+              network blip). Hides the SSO button; prompt user to refresh. */}
+          {configError && !appConfig && (
+            <div style={{ marginTop: 16, padding: '10px 14px', background: '#fef3c7', border: '1px solid #fde68a', borderRadius: 12, fontSize: 13, color: '#92400e', display: 'flex', alignItems: 'center', justifyContent: 'space-between', gap: 8 }}>
+              <span>{t('login.configLoadError')}</span>
+              <button
+                onClick={() => window.location.reload()}
+                style={{ background: 'none', border: '1px solid #d97706', borderRadius: 8, padding: '4px 10px', fontSize: 12, fontWeight: 600, color: '#92400e', cursor: 'pointer', fontFamily: 'inherit', whiteSpace: 'nowrap' }}
+              >
+                {t('login.configLoadRetry')}
+              </button>
+            </div>
+          )}
+
           {/* Demo login button */}
           {appConfig?.demo_mode && (
             <button onClick={handleDemoLogin} disabled={isLoading}
diff --git a/client/src/sw.ts b/client/src/sw.ts
index d1ea15a4..92fa1a1a 100644
--- a/client/src/sw.ts
+++ b/client/src/sw.ts
@@ -7,7 +7,7 @@ import {
   matchPrecache,
 } from 'workbox-precaching';
 import { registerRoute, NavigationRoute } from 'workbox-routing';
-import { NetworkFirst, CacheFirst } from 'workbox-strategies';
+import { NetworkFirst, CacheFirst, NetworkOnly } from 'workbox-strategies';
 import { ExpirationPlugin } from 'workbox-expiration';
 import { CacheableResponsePlugin } from 'workbox-cacheable-response';
 import {
@@ -135,6 +135,15 @@ function applyConfig(cfg: SwCacheConfig): void {
   osmStrategy    = buildTilesStrategy(cfg);
 }
 
+// Apply authRedirectPlugin to the public app-config endpoint so a ZT redirect
+// surfaces as AUTH_REQUIRED (401) instead of causing a silent JSON parse failure
+// on the login page, which would hide the SSO button.
+registerRoute(
+  /\/api\/auth\/app-config$/i,
+  new NetworkOnly({ plugins: [authRedirectPlugin] }),
+  'GET',
+);
+
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 registerRoute(/\/api\/(?!auth|admin|backup|settings).*/i,  { handle: (o: any) => apiStrategy.handle(o) },   'GET');
 // eslint-disable-next-line @typescript-eslint/no-explicit-any